The present invention relates to a spiral drill with indexable inserts comprising a holding shank, a nose portion with insert pockets for the receipt of a central insert and a peripheral insert, and a spiral part which comprises two spirally curved ribs with a coolant channel provided in each such rib.
In spiral drills it is possible to supply liquid through coolant channels to openings near the cutting edges, which facilitates chip formation and lowers friction in the flutes. In order not to lower the torsion stiffness and give an undesirable coupling between axial force and torsion angle, the drill can often be made with two spiral coolant channels as shown in the patents SE-335111 and EP-0 188 035, located between the flutes in the ribs where they are least detrimental to the strength of the drill body. Those patents also show how a drill can be made from a such a spiral part joined to a separately made shank part with different locations of coolant channels.
It is also known through Swedish Patent 194706 to make drills with indexable carbide inserts in pockets on a steel body, where it is possible to utilize a limited number of insert sizes for a large number of drill diameters by using two or more asymmetrically located indexable inserts, one of which is a center insert close to the center line of the drill and one of which is a peripheral insert close to the periphery of the drill.